There is no chance with the existing header that I can go as short as 22".
I have to go from where the pipes are jioned and level with the ground.
But as it is an larger diameter a longer length will be necessary anyhow.

I am tempted to speculate how to improve the design you have already tested, clearly it is wrong in several ways, so one wonders how much it could be improved..... but for now it will be better to forget about it. I do appreciate you sharing the results.

I have just finished my test header.
Approximately 28" primaries with 45mm OD, 42mm ID. 1,8"- 1,65".
14" secondaries that can be cut down or lengthened but this length fits the exhaust system. 51mm OD, 48mm ID. 2"-1,89".
The last pipe is 63mm OD, 60mm ID. 2,5" and connects to the exhasur system where there is a empty cat a bit down.
I will probably make an insert in my lathe and test with 54mm ID.
Then I will have 6mm bigger diameter for each pipe. 42-48-54-60mm.
I will try it on the dyno this weekend and go from what I see there.

To say it looks like this header would be a lie but the difference is cosmetic and my header ends in a straight pipe.

Erland

I must have built over 2 hundred sets of that cup ford header from 95 to 98 until till Yates, Rousch and Elliotts built their own. 1.75 @8 or 10 inches, and 188 for 11inches more of primary and 8-12" of 225" and a 2.5" choke would handle 780-800hp. The original design was for restrictor engines and primaries were straight 175 and secondaries 2" and chokes could be 225" for 450hp. Tried 165 primaries off the head but the ports were too large and the flow loss was too much.. Heck, the 175 stuff was probably 5% smaller than the ports on the open motors!
The ports were too big.
They run bigger stuff now and the faster tracks don't need 421`s anymore. I think the cup stuff is over 850hp now. I really don't know.
So that's enough header for a 375hp what 160inch 4 banger? How big is your port again?
:

That's a brilliant example. The ratios of sizes and lengths is WORTH NOTING.

42 to 48, only 30% increase in area.
IMO the working range is about 30%-50% roughly, so reasonable choice but it may be worth trying a larger step-up there to get more mid-top boost. If that be smaller primaries or larger secondary I don't know, but if the secondary size seems right in testing then that might mean smaller primaries should be tried.
The step from secondary to final size is over 50%, but that's ok, will be easy to test a smaller choke in there.

I think.....the longer the primaries are in relation to secondaries, the larger the step-up % will be, at least with this firing order and arrangement.

That's a brilliant example. The ratios of sizes and lengths is WORTH NOTING.

When I was asked to do a 421 for the Pro-Stock engines back in 1998, I simply built the same header lengths but sized it by
simply comparing valve diameters and scaled up the tubing diameters. 2.12" off the head 421 and a 3" choke in the collector.
Warren Johnson was the first PS to run 200mph the first time out with his set. I was told he tried opening up the final choke and lost power each time.
It is also interesting that a 421 header can always use a final choke a .250" smaller than a 4into1 on a V8 in the 6000-8000rpm band. (That's my headers and work, not comparing brands...) But a 421 on a 2.3 litre 4 banger is somwhere around 1.7-1.9".

yeah, I might have figured wrong, but anyway it's real small.
I think you are right on a v8 the tri-y lets you use a smaller choke, but on a four banger it's opposite, due to firing order. You build it odd-fire then perhaps it's possible. The jap bikes and hondas that pair 1-2 and 3-4 often use a relatively small choke. Odd-fire each Y can resonate up to the first harmonic and still work, but paired 1-4 and 2-3, each y pair needs to run in the second harmonic. I can't really explain it right, but that's where the difference lies if there is one.

Fascinating discussion as always. I've never really understood completely what happens on the exhaust side. I don't feel too bad, as I am guessing I'm not the only one!

I think that an inline four with 180-degree equally spaced pulses should maybe have a different kind of 4-2-1 header than a cross-plane V8 bank?

One though I've had is that the required power-band bottom-end rpm should put some requirements on the minimum primary length in a I4 4-1 header. I think that the 180-degree exhaust blowdown interference is the big problem at lower rpms. The exhaust valve opening for one cylinder will create a high-pressure pulse that moves at the speed of sound (adjusted from mean flow effects) and that will potentially arrive in the cylinder preceding it in the firing order during that cylinder's overlap period. This is to be avoided by my logic. Therefore, the minimum rpm at which the 4-1 header can "work" is the rpm at which the crankshaft rotating (exhaust duration - 180) degrees starts taking less time than the high pressure pulse traveling from the later firing cylinder's exhaust valve to the earlier firing cylinder's exhaust valve.

Because the 4-2-1 header connects the 360-degrees apart cylinders first, I am guessing the path length thru the primaries and secondaries (the 180-degree interference path) is always so long that the 4-2-1 header starts "working" at a very low rpm, where "working" is defined as avoiding the 180-degree exhaust blowdown interference. The primary+secondary is almost always going to be long enough.

I'm wondering how much of the 4-2-1 headers reputation as producing low-end torque simply comes from this effect?

[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]

I'm wondering how much of the 4-2-1 headers reputation as producing low-end torque simply comes from this effect?

Well that is the reality. It attenuates pressure waves in the system and reduces reversion by a large factor. I think I already posted in this thread but in the past, folks knew they could put 421 collectors on their 4into1 headers and make more torque but they also knew they would give up power upstairs.
The same thing would happen with 4into1 headers, the longer you make them the more torque and less power. Well if you shorten the primaries you can get both with a 421. You can also protect torque on a 4into1 with smaller chokes but I have not seen where that can do as good a job as a 421 design. There are other things happening with 4into1 merged collectors and I have discussed that in other threads.

Over the years, one of the biggest factors I ran into were highly evolved engines with exhaust ports and valves that were way too large. Usually a leftover from original castings and sizing. It was necessary to make things larger when you don't have springs, light valves,rollers,cam designs etc. to increase flow. Bigger always made more power. You have to move the air...
Fast forward and many applications are dealing with valves and ports that are way too large. It is hard for many builders to go "smaller" in both the mental aspect not too mention the physical difficulties. It is hard and expensive to make ports smaller, and the mental attitude just re enforces the issue. So cams timing and whatnot are all compromised dealing with reversion and trying to still move air upstairs. A 4into1 has to be long enough to keep pressure waves from hurting the other cylinders at the lowest rpm the engine is used for. (This is more important to me than the overlap tuning) That is the only way to battle reversion besides closing valves earlier or opening them later.....
A 421 can greatly reduce reversion without flow loss (if built right), so you can have both. I believe the primaries help a 421"tune" upstairs. The shorter I can make the primaries the header runs better upstairs. Problem is getting primaries short enough to run well past 9k rpm, it is very difficult to build a 421 header with 8-10inch primaries...The secondary length can usually be lengthened to cover the bottom end of the power curve.
I have run into efforts that simply can not change from a 4into1 to a 421 on a 4 cyl as the 421 changes things so much the combinations fall on their face. They require a lot of cam changing and other aspects changed to see any benefit. Most do not want to go there and I have to walk away. I believe they are missing a lot.
Most 4 cylinder engines I run into are in that category. The headers and ports are way too large and they have severe reversion problems and a 4into1 is not able to help them like a 421 can.
There is another factor you run into here is 4 valve engines and there are a lot more of them in 4cyl than 8cyl. They breath like crazy and do not need anywhere near the cam timing to run the same rpm as a 2 valve engine. As a result they do not run into reversion problems as soon. This allows the engine builders to bigger headers and rely solely on wave tuning to tune upstairs or not even bother "tuning" at all and still make power...
Basically there is less need to develop a exhaust system that can reduce reversion, so they don't.
I know this is rambling but I have to go.

4-2-1 Exhaust System
One option to significantly reduce residual gas is the adoption of a 4-2-1 exhaust system. As shown in Fig.3, when the exhaust manifold is short, the high pressure wave from the gas emerging immediately after cylinder No. 3’s exhaust valves open, for example, arrives at cylinder No.1 as it finishes its exhaust stroke and enters its intake stroke. As a result, exhaust gas which has just moved out of the cylinder is forced back inside the combustion chamber, increasing the amount of hot residual gas. With a short exhaust manifold, the high pressure wave arrives at the next cylinder within a short amount of time, causing this adverse effect to continue from low to high engine speeds. However, with a long 4-2-1 exhaust system, since it takes time for the high pressure wave to reach the next cylinder, the effect mentioned is limited to extra-low engine speeds, making the reduction of residual gas at almost all engine speeds possible.

In addition, a pipe length of over 600mm was necessary to elevate actual-use torque, but space was saved by adopting a loop shape.

[b]Paradigms often shift without the clutch[/b] -- [url]https://www.youtube.com/watch?v=cxn-LxwsrnU[/url]